Sudden opening or closure of a control valve, or tap, can cause a pressure surge or spike in plumbing as a result of forcing a fluid in motion (or, in some conditions, a gas) to stop or change direction suddenly. This phenomenon is called water or fluid hammer, and it can cause ruptures and leaks in pipes and fittings. Water hammer creates pressure waves that travel upstream and downstream of the closed/opened taps at nearly the speed of sound. There are a number of standard techniques that attempt to minimize the pressure spikes resulting from water hammer. In pipe networks, for example, common techniques to address water hammer include use of surge vessels, equilibrium tanks, pressure relief valves, and suction lines around the booster pump. In residential and light commercial/industrial applications, an air chamber and water hammer arrestor may be used for water hammer control.
FIG. 1 shows a prior art pipe network that employs an air chamber to address undesirable pressure surges associated with water hammer. As shown in FIG. 1, this is a conventional technique wherein a short vertical section of pipe is filled with trapped air. In this scenario, when a valve is suddenly closed, the air chamber acts as a shock absorber. Air in this chamber compresses and cushions the resulting shock. The disadvantage of this conventional technique/device is that after time, the air pocket is eventually absorbed into/by the water, which renders the device ineffective. To remedy this limitation, one must drain water out of the system to recreate the air pocket. Referring to FIG. 2, a prior art arrestor device designed to address water hammer in a pipe network is shown. As shown in FIG. 2, this solution to water hammer is similar to that of the air chamber of FIG. 1, with the exception that the air pocket in the arrestor is separated and sealed from the water by a piston with an “O” ring or diaphragm so that the air cannot be absorbed by water. The air pocket for this type of water hammer control device is pressurized to a certain limit. One disadvantage of this “arrestor” technique/device is that the pressure level of the air pocket is typically too high for the device to work properly for low pressure applications. Another disadvantage of this device is that the moving piston generally makes it noisy. Furthermore, both the air chamber and water hammer arrestor devices have the disadvantage of being metallic (usually copper); thus, they are susceptible to corrosion and erosion.